Speakers at the TEDGlobal conference have been debating the positive use of drones in society.

Delegates heard how drones, more usually seen as military tools, are increasingly playing a positive role in civilian life

They are offering new ways of transportation and carrying out vital conservation work.

But, warned one speaker, far stricter controls are needed over the use of such machines in war.

Sci-fi author Daniel Suarez called for international treaties to limit the use of autonomous combat drones that are increasingly being developed by nations such as the US and Israel.

"There are tonnes of great uses for unmanned drones but we need a framework for robotic weapons as it puts too much power into too few hands," he said.

"Increasingly combat drones are making lethal decisions about human beings."

In 2011 US drones created 300,000 hours of video surveillance, for example.

"This is outstripping the human ability to review it all so increasingly people will rely on visual intelligence software," said Mr Suarez.

He also warned of the threat of anonymous war, where terrorists or criminals could launch drone attacks which would be difficult to trace back. "Such a war would tilt the geo-political balance on its head," he said.

Delivering supplies

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Tests in Haiti showed how drones can be used to deliver supplies

On a more positive note, delegates heard how drones can play a vital role in civilian life.

Andreas Raptopoulos is currently building a network of drones to provide vital supplies to hard-to-reach places.

Acrobatic drones

At the TEDGlobal "flying lab", quadrirotors developed at the Swiss Federal Institute of Technology are being put through their paces all week.

Demos show the drones performing a variety of tasks, including acrobatic dancing, batting balls and balancing poles.

The team will also attempt to build a tower of Lego bricks using the drones.